[swift2objc] More built in declarations

[liamappelbe]

I'm working on a PR that adds all the Apple Foundation symbols to all swift2objc parses. This is a self-contained part of that change that expands the number of built in toll-free bridging types we support.

First, fix a bug in parse_symbols_map.dart, skipping parsing for any symbols we've already seen. Otherwise when parsing Foundation we overwrite a lot of the built in declarations.

Next, I noticed a lot of the IDs in Foundation start with c:objc(cs), and AFAICT these are all toll-free bridging types. So I added a special case in the parser that detects these objects and returns a BuiltInDeclaration instead of actually trying to parse the object. This avoids generating a lot of unnecessary wrappers.

Finally, I parsed all of Foundation, and printed out all the IDs of this form, then hard coded them in the built in list. This significantly speeds up and simplifies parsing of Foundation, and also means that we can get pretty far without even needing to parse Foundation. I'm currently testing whether this change makes swift2objc powerful enough for MVP without the need for the bigger change that this PR was peeled off of.

[github-actions]

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// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

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pkgs/jni/lib/src/third_party/generated_bindings.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

[coveralls]

coverage: 81.701% (+0.1%) from 81.584%
when pulling 71b12fd on swift2objc_more_built_ins
into 9d68fa4 on main.